1. Field of the Invention
The present invention relates to a molded part having a slanted surface, a curved surface and/or a sculptured surface, which has a fine pattern. In addition, the present invention also relates to a die for forming the part; an optical element using the molded part; and an optical device (such as optical scanning devices, image displaying devices and optical pickup devices) using the optical element.
2. Discussion of the Background
In general, it is important to control reflection of light at the surface of an optical element. In attempting to prevent reflection at the surface of an optical element, a technique such that a multiple dielectric layer is coated on such a surface has been used. Specifically, such an optical element is prepared by performing plural processes such as preparation of a part by a molding method (such as injection molding) and formation of such a multiple dielectric layer on the surface of the part using a coating device. Since these processes take a long time, the resultant optical element has a high manufacturing cost.
Recently, in attempting to solve the cost problem, a technique in that fine patterns are formed on the surface of an optical element to prevent reflection of light at the surface of the optical element has been used. Such fine patterns are formed on the optical element by using a die, on the surface of which fine patterns are formed by a mechanical method of a method including a semiconductor process. Namely, fine patterns corresponding to the fine patterns formed on the surface of the die are formed on the surface of the molded optical element, which is made of a material such as resins and glass. Here in after, this method is sometimes referred to as a mold transfer method.
Published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2003-270569 discloses a scanning optical system and an image forming apparatus using the system. It is described therein that excellent optical performance is obtained by appropriately setting the array direction of a fine structural grating in accordance with the polarization plane of an incident luminous flux and reducing the influence of the structural double refraction of a fine grating structure. Specifically, in the scanning optical system as illustrated in FIG. 1B, a luminous flux emitted by a laser light source 1 is deflected by a deflecting means 5, and the deflected luminous flux is focused on a surface 7 while scanned by a scanning optical means 6. The scanning optical means 6 includes a first scanning lens 6a having one or more optical surfaces having a fine structural grating 8 (including a grating portion 81 and a non-grating portion 82). The grating pitch of the fine structural grating is shorter than the wavelength of the luminous flux and the fine structural gratings are arrayed in parallel over the entire surface of the scanning lens 6a. 
In addition, recently fine patterns such as a number of fine grooves are formed on the surface of a molded part to control the wettability and/or the friction coefficient of the surface. Such fine patterns are typically formed by a mold transfer method.
When such fine patterns are formed by a mold transfer method, a problem in that the die used cannot be well released from the molded part and thereby the quality of the resultant fine patterns is degraded (i.e., the desired function cannot be imparted to the molded part) occurs.
In addition, when the slope of the surface of the molded part is sharp relative to the die releasing direction (i.e., when the angle formed by the slope and the die releasing direction is large as illustrated in FIG. 3), a problem in that fine patterns such as rectangular grooves cannot be formed on the molded part occurs.
Referring to FIG. 1A, the background art disclosed in JP-A 2003-270569 uses the scanning lens 6a having one or more optical surfaces having the fine structural grating 8 including grating portions (i.e., grooves) 81 and non-grating portions 82, which are arranged so as to be parallel to each other. Thus, the scanning lens 6a has fine patterns which are slanted against the curved surface of the lens. When such fine patterns are formed by a mold transfer method, a problem in that the die used cannot be well released from the molded part and thereby the quality of the resultant fine patterns is degraded occurs. Specifically, as illustrated in FIG. 1B, a light beam is slantingly launched into the surface of the scanning lens 6a. Therefore, it is preferable that the grooves 81 face the light beam (i.e., the grooves are also slanted) to improve the optical property of the lens 6a. When such grooves are formed by a mold transfer method, it is hard to release the die from the molded part (lens) because the die releasing direction is different from the direction of the grooves. Therefore, a problem in that the die used cannot be well released from the molded part and thereby the quality of the resultant fine patterns is degraded occurs.
Particularly, when a part having a curved surface having rectangular grooves thereon is prepared by a mold transfer method, releasing of the die used is very difficult because the projections of the die cannot be released from the grooves formed on the surface of the part. Specifically, when the die releasing direction is the same as the direction of the rectangular grooves as illustrated in FIG. 2, releasing of the die can be well performed. However, when the die releasing direction is largely different from the direction of the rectangular grooves as illustrated in FIG. 3, releasing of the die is very difficult. In this case, the grooves cannot be well formed (i.e., the grooves are damaged). In other words, only parts having steps (as illustrated in FIG. 4) on the surface thereof can be molded by a mold transfer method.
Because of these reasons, a need exists for fine patters, which can be well formed on slanted surfaces, curved surfaces and sculptured surfaces by a mold transfer method to improve properties of the surface such as reflection preventing property, wettability and friction coefficient.